Technical Article

Power Adapter Overheat Protection Circuit

Heat resistance and fire performance of the
power adapter is not only directly related to the reliability and service life
of the power adapter, but also directly related to the degree of the risk of
fire, related to the safety of the lives and property of the user.Power
adapter main heat source Schottky rectifier diodes, high-frequency switching
transformers, power MOS filtering electrolytic capacitors, power MOS
high-frequency transformer and rectifier Schottky diode temperature rise is
more prominent.Power
adapter damage due to overheating, not only requires the use of
high-temperature characteristics of a good electronic components in the design
of the switching power supply adapter, also asked the printed PCB board, the
heat sink, high-frequency transformer design is reasonable, advanced production
technology, and the need to take in order to prevent overheatingprotection measures, which are designed to
guarantee the security must have the condition.In addition to the
selection of leakage current, short storage time power MOS in order to suppress
the temperature rise of the power adapter, you need to give the power MOS
installation of the heat sink.Proved MOS tube to install the heat
sink, the stability of the power adapter will greatly improve the loss rate was
significantly lower.The
role of the electronic switch overheat protection measures is easy to heat in
the power adapter components or power supply enclosure temperature exceeds the
set limit before you disconnect the AC adapter AC input line, or forced to shut
down the modulation pulse output, stop the high-frequency oscillation.Power adapter overheating protection can be divided into the following categories: automatic
reset, manual reset type, can not be updated, reset and various other types of
protection equivalent to overheat.The overheating protection
switching power supply constitutes a whole, need to pay attention to the
placement accept the distance from the heat source, can be replaced Difficult.Placed
the most basic requirement is not subject to mechanical impact, easy removal;
protection function and polarity, cord-connected, plug without polarity
equipment should have two leads overheat protectioncontrol; protection circuit is
disconnected, does not affect the normal operation of the power adapter, but
can not cause a fire or damage to the electrical equipment.The usually power adapter circuit
board area and the plastic housing space are relatively small, has some
difficulties with overheating protection.If the overheating protection is
difficult to assemble into, temperature fuse or thermistor can be used as a
thermal protector.Paste
it on the the heatsink surface of the high-frequency transformer or power MOS,
overheating protection switch will automatically cut off the power when the
temperature rises to a certain value, or forced to shut down modulation pulse
output stop the high-frequency oscillation.If the
power adapter with a control driver IC with overheating protection function,
then do not need to add any external components or only need to add very few
external components, can play overheat protection.Because the power adapter control
driver IC has a built-PN junction temperature sensor containing thermal
shutdown circuit.PN junction temperature sensor does not
have a built-driven IC, connected to a temperature sensor element in its
external.The driver IC
thermal shutdown circuit, overheat protection becomes very simple, and
integrated circuit itself, the price is also very low, the cost performance is
very high.